na-adjective, noun
mediocrity; imbecility; foolishness
Rare literary term for a state of being mediocre or foolish. In modern Japanese, 凡庸 or 愚かさ are more common.
彼の庸愚な振る舞いに皆が呆れた。
Everyone was appalled by his foolish behavior.
庸愚の身では、その任は務まらない。
A person of mediocrity cannot fulfill that duty.